As the chemicals industry moves away from petroleum-based materials, the efficient formation of glycols from renewable sources is a highly desirable reaction pathway. Ethylene glycol is a precursor to polyesters and polyethylene terephthalate (PET), while propylene glycol is widely used in the chemicals industry. These glycols are currently produced from petrochemicals, however they can also be derived from renewable biomass.
The concept of converting sugar alcohols to polyols, mainly ethylene glycol (EG), propylene glycol (PG), and glycerin (GLY), has been known for over seven decades. Many research papers and patents have been published on this topic. Besides the three major products, minor products include primary alcohols, such as ethanol and propanol, butandiols, even trace adols and acids. Depending on reaction conditions, gaseous products will include CO2, CO, and methane. A common feature in these processes is the presence of water as a solvent.
The main obstacles to commercialization of the process include the low selectivity towards the marketable products and high production cost because of elevated operation pressure and temperature, usually over 100 bar and 200° C., and difficulties in product separation. Also, it was found that higher pH is necessary to increase the reaction rate and the product selectivity. This further worsens proper operation of heterogeneous catalyst and could result in the disintegration of supports, as well as leaching and sintering of active metals. These conditions render a great challenge to commonly available materials for supported heterogeneous catalysts.
Prior work has identified supported Ru-, Rh-, Ir-, Ni-, Re- and Pd-based materials as catalysts for glycol production from ligno-cellulosic polyols such as sorbitol and xylitol. For example, U.S. Pat. No. 6,291,725, issued Sep. 18, 2001, to Chopade et al., disclosed Ru on alumina, zirconia and carbon support; PCT Publication No. WO 2008/071616, filed on Dec. 6, 2007, by Hoffer et al., disclosed a catalyst comprising iridium on carriers selected from carbon, titanium oxide and calcium carbonate for EG, PG production from polyols. However, there have been no reports of an economically viable catalyst with sufficient selectivity to produce glycols to be widely implemented in the chemicals industry.
A method to prepare polyacid stabilized zirconia support, which is hydrothermally stable in aqueous phase hydrogenation and hydrogenolysis reactions, is described in U.S. Patent Publication No, 2011/0301021, Mar. 3, 2010, by Lui et al. The process for conversion of sugar, sugar alcohol, or glycerin to short chain glycols, EG and PG, by using the polyacid stabilized zirconia is described in U.S. Patent Publication No. 2011/0319672, filed Mar. 3, 2010, by Lui et al. The active metals, group (VIII) and group 11 and combinations thereof, were described as catalyst on the promoted zirconia support for the process, specifically, Ni, Cu, and tin-promoted Ni. U.S. Patent Publication Nos. 2011/0301021 and 2011/0319672, are incorporated by reference herein in their entirety.
It is desirable to increase the EG and PG selectivity during the hydrogenolysis of polyols.